Seriously?

In study 1, a certain historic data set is presented. The data set shows an underlying variation around a fairly strong trend line. The trend line is removed, for a variety of reasons, and the data set is presented normalized or de-trended.

In study 2, researches take the normalized, de-trended data and conclude … wait for it … that there is no underlying trend in the natural process being studied. Am I really understanding this correctly? I think so:

The briefest examination of the Scotland speleothem shows that the version used in Trouet et al had been previously adjusted through detrending from the MWP [Medievil Warm Period] to the present. In the original article (Proctor et al 2000), this is attributed to particularities of the individual stalagmite, but, since only one stalagmite is presented, I don’t see how one can place any confidence on this conclusion. And, if you need to remove the trend from the MWP to the present from your proxy, then I don’t see how you can use this proxy to draw to conclusions on relative MWP-modern levels.

Hope and change, climate science version.

Postscript: It is certainly possible that the underlying data requires an adjustment, but let’s talk about why the adjustment used is not correct. The scientists have a hypothesis that they can look at the growth of stalagmites in certain caves and correlate the annual growth rate with climate conditions.

Now, I could certainly imagine (I don’t know if this is true, but work with me here) that there is some science that the volume of material deposited on the stalagmite is what varies in different climate conditions. Since the stalagmite grows, a certain volume of material on a smaller stalagmite would form a thicker layer than the same volume on a larger stalagmite, since the larger body has a larger surface area.

One might therefore posit that the widths could be corrected back to the volume of the material deposited based on the width and height of the stalagmite at the time (if these assumptions are close to the mark, it would be a linear, first order correction since surface area in a cone varies linearly with height and radius). There of course might be other complicating factors beyond this simple model — for example, one might argue that the deposition rate might itself change with surface area and contact time.

Anyway, this would argue for a correction factor based on geometry and the physics / chemistry of the process. This does NOT appear to be what the authors did, as per their own description:

This band width was signal was normalized and the trend removed by fitting an order 2 polynomial trend line to the band width data.

That can’t be right. If we don’t understand the physics well enough to know how, all things being equal, band widths will vary by size of the stalagmite, then we don’t understand the physics well enough to use it confidently as a climate proxy.

This band width was signal was normalized and the trend removed by fitting an order 2 polynomial trend line to the band width data.

The only thing I can think of (and it’s been years since I’ve delved into this level of mathematics, so I may simply be talking out of my ass on this) is that an “order 2 polynomial” would be based on the cross-sectional area of the cone (i.e., r^2–makes it 2nd order). They’d have to make some guesses and approximations, but maybe they’ve found a polynomial that does fit.

Of course, they could have just as easily found a 2nd degree polynomial that forces the data to fit their preconceived conclusions, so there you go. Without seeing the details (raw data, algorithms, mathematical justifications for certain modeling assumptions, etc.), there’s no way to know what is really happening behind the scenes.

But we should just trust them. They know what they’re doing….

Jim

It seems it would be a lot easier to create a model for the growth of a stalagmite that is reasonable than for the entire climate system of Earth. Of course, even in the case of the stalagmite it would be still nothing more than an educated best effort.

Another guy named Dan

I would be interested to see how well their stalagmite data correlates to tree rings in the immediate environs.

My thought is that it seems to me that both processes are driven at least as much by amount of rainfall and atmospheric CO2 content as by temperature. It would be begging the question to assume that high CO2 correlates to high temperature in the proxy measurement, then turn around and use that measure to determine that a temperature trend is caused by CO2.

Luke

Do you think could re-post this, except in English? 🙂
All kidding aside though, I am no expert on the topic so I’m wondering if someone could water down what he is trying to say here?